package vip.meeet.algorithm.dp;


public class Num70 {

    public static void main(String[] args) {
//        System.out.println(climbStairs(3));
        System.out.println(climbStairs2(61));
    }

    public static int climbStairs(int n) {
        if (n == 0) {
            return 0;
        }
        if (n == 1) {
            return 1;
        }
        if (n == 2) {
            return 2;
        }
        int[] dp = new int[n];
        dp[0] = 1;
        dp[1] = 2;
        for (int i = 2; i < n; i++) {
            dp[i] = dp[i - 1] + dp[i - 2];
        }
        return dp[n - 1];
    }

    public static int climbStairs2(int n) {
        if (n == 0) {
            return 0;
        }
        if (n == 1) {
            return 1;
        }
        if (n == 2) {
            return 2;
        }
        if (n == 3) {
            return 4;
        }
        int[] dp = new int[n];
        dp[0] = 1;
        dp[1] = 2;
        dp[2] = 4;
        for (int i = 3; i < n; i++) {
            int med = (dp[i - 3] + dp[i - 2]) % 1000000007;
            dp[i] = (med + dp[i - 1]) % 1000000007;
        }
        return dp[n - 1];
    }
}
